Nitrosamines capable of inducing the formation of liver and kidney tumors in rats will be administered in single or multiple doses. The effect of the dosage level on the activity of ornithine decarboxylase and the polyamine content of the target tissues of the carcinogens will be determined. Relationships between the incidence of tumors and ornithine decarboxylase activity will be investigated by modifying the enzyme activity during the course of tumor development. Enzyme activity will be altered by dietary supplements of vitamins, by the feeding of toxicants and by the administration of enzyme inhibitors. The effect of nitrosamines on the synthesis of macromolecules by target tissues and the time course of changes in the synthesis of polyamines and macromolecules will be compared.